This plugin is specific to AM123 but could be used as a base for similar operations.
It is used for stocknumber computation.

If the user send an empty string,
we return a simple incremented stocknumber.
If a prefix is submited,
we look for the highest stocknumber with this prefix,
and return it incremented.
In this case,
a stocknumber has this form : "PREFIX 0009678570".
- PREFIX is an upercase word - a space separator - 10 digits,
with leading 0s if needed